Are the north and south horizons not equally distant?

Dear Cecil:

Would you give me the straight dope on the rumor I once heard that the northern and southern horizons are not equidistant from the observer? And also that they are not equidistant to the easter and western horizons? (This assumes that the observer is standing on a perfectly flat surface.)

Cecil replies:

Cecil replies:

I don’t know that this is what I would consider a "rumor," T., but let’s not sweat the small stuff.

In the Northern Hemisphere (except near the North Pole) the northern horizon is slightly farther away from you than the southern horizon, owing to the fact that the earth is not perfectly spherical, but ellipsoidal, i.e., fatter around the equator than it is around a meridian (a circumference that includes both poles). You may want to get an egg out of the refrigerator and think about this; otherwise just trust me.

The eastern and western horizons are equidistant from an observer, but they are closer than the northern horizon and farther away than the southern horizon. (Got that?) Having performed my usual superhuman calculations, I can state that for a person five feet tall standing on a raft in calm waters at 45 degrees latitude in the Northern Hemisphere, the distance to the northern horizon exceeds that to the southern horizon by a total of … four inches. Large charge. Still, it is with just such minutiae that we impress the babes at the boathouse.

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